1. Field of the Invention
The present embodiments generally relate to the field of implantable medical devices and in particular to identifying a suitable pacing site for such implantable medical devices.
2. Description of the Prior Art
It is generally regarded as important within the technical field of implantable medical devices (IMDs) to achieve an appropriate positioning of cardiac leads in or in connection with the ventricles of a heart for a patient. For instance, the position of a left ventricular coronary sinus lead has an impact on the outcome of cardiac resynchronization therapy (CRT) provided by an IMD to which the lead is connected. Most physicians implanting such leads in CRT patients, though, routinely go for a lateral or posterior-lateral vein that seems accessible for the particular patient. However, the most accessible vein might not be the most suitable pacing site from therapy point of view. A lot of focus has therefore been directed towards finding suitable pacing and implantation sites for cardiac leads and in particular left ventricular coronary sinus leads.
U.S. Pat. No. 7,142,919 discloses an IMD with a multi-electrode ventricular lead. Optimal pacing site is determined in connection with CRT by testing each of the electrodes of the multi-electrode ventricular lead as pacing electrode. Optimal pacing site and electrode is selected based on the output of a mechanical sensor, such as accelerometer or pressure sensor, attached epicardially on the left ventricle or from intracardiac electrograms (IEGM).
U.S. Pat. No. 7,330,759 relates to an IMD adapted for biventricular CRT stimulation and includes an impedance detection unit that is employed for selecting optimal biventricular stimulation. It is disclosed that optimal electrode position during implantation can be determined from determined intracardiac impedance or optimal stimulation electrode configuration can be determined following implantation from the intracardiac impedance. The relevant intracardiac impedance parameter employed in the site or electrode optimization is representative of the maximum acceleration to which the blood is exposed to in the heart.
US 2008/0249585 discloses an IMD suitable for CRT stimulation. The IMD has an impedance detection unit arranged for determining intracardiac impedance for the purpose of calculating a quality factor that is equal to the quotient of a first intracardiac impedance value determined for an intrinsic cardiac cycles sequence and a second intracardiac impedance value determined for a paced cardiac cycles sequence. The calculated quality factor can be used for determining optimal implantation site for a left ventricular lead by selecting the implantation site that gives the highest quality factor.
US 2008/0249375 relates to a pacing system analyzer (PSA) employed for selecting optimal lead position for a left ventricular lead during implantation. Impedance signals are recorded at different lead positions and processed to determine contractibility of the cardiac muscle, ejection fraction or pre-ejection time period. The position resulting in best contractibility, ejection fraction or pre-ejection time period is selected.
US 2008/0004667 relates to the selection of electrodes and pacing configuration parameters used to pace a heart chamber. A change in the hemodynamic state of the patient is detected and is used to determine a distribution of an electrical and/or mechanical parameter related to the contractile function of the heart chamber with respect to locations of multiple electrodes. A pacing output configuration is selected and the heart chamber is paced according to this pacing output configuration.
There is still a need for a technique that can be used to identify optimal pacing electrode and/or implantation site of a ventricular lead and in particular such a technique that does not require the usage of dedicated sensors or complex processing in the IMD.